1. Field of the Invention
The present invention relates to a flat panel type display device, such as a liquid crystal display device or an organic EL display device, which is used for an information equipment, such as a computer or a portable terminal, or for an Audio Visual equipment such as a large screen television.
2. Description of the Related Art
FIGS. 7A and 7B simply show the structure of a conventional liquid crystal display device. FIG. 7A is a front view and FIG. 7B is a sectional view taken along the line A-A′ of FIG. 7A.
The liquid crystal display device includes a pair of substrates which are a TFT substrate 1 having a pixel matrix circuit and a driver circuit, and an opposite substrate 2 on which a color filter is formed. The substrates 1 and 2 are opposite to and bonded to each other, and a liquid crystal material 5 is sealed in a gap between the substrates by a sealing material. Reference numeral 3 denotes an external connection terminal for connecting a driver circuit formed on the TFT substrate 1 to an external power source circuit or the like.
The liquid crystal 5 is sealed in by a sealing material 4 formed on a peripheral portion of the substrate 1 or 2. The sealing material 4 is formed on the surface of the substrate 1 or 2 by a dispenser system, a screen printing method, or the like. A liquid crystal injection port is formed in a part of the sealing material 4, and is sealed with an adhesive 6 after the liquid crystal 5 is injected.
Since the sealing material 4 is formed on the surface of the substrate 1 or 2, the size of the substrate becomes large by the width of the sealing material 4 itself or a margin in a sealing material providing step. For example, a nozzle diameter of a dispenser is about 100 to 300 μm, and a sealing material with this width is linearly drawn on the surface of a substrate resulting that the width of the sealing material 4 becomes about 1 mm when the substrates 1 and 2 are bonded to each other.
As shown in FIGS. 7A and 7B, in the conventional device, the sealing material for sealing the liquid crystal material is formed on the surface of the substrate, so that the area of the substrate becomes larger than an effective display portion, which prevents miniaturization of the display device.
At present, a manufacturing technique of a polysilicon TFT has been established, and a liquid crystal display device in which a driver circuit and a pixel matrix circuit are integrated, is in plentiful supply. However, a substrate area becomes larger than an effective display region by the formation of the driver circuit. It is desirable that a space other than a display region is as small as possible in view of miniaturization of a device or getting multiple pieces. Thus, a method of disposing a sealing material on a driver circuit has been employed.
However, since glass filler for regulating a cell gap (an interval between substrates) is generally mixed in the sealing material, when the sealing material is disposed on the driver circuit, the filler gives damage and stress to the driver circuit. Moreover, since the driver circuit has a surface roughness larger than a pixel matrix circuit, it is very difficult to uniformly keep the cell gap on the driver circuit by the filler.
Moreover, an active type display device has a problem of heat generation since an insulating substrate, such as a glass substrate or quartz substrate, is used as a substrate. The thermal conductance coefficient of the sealing material is relatively small so that heat radiation is insufficient, and there is also a problem of detachment due to heat expansion and contraction.